Thermal conductive grease

ABSTRACT

A thermal conductive grease used for diffusion of heat generated in electronic appliances is provided. The thermal conductive grease comprises: (A) a base oil having a viscosity of 112 to 770 mm 2  at 40° C. and comprising a copolymer of an unsaturated dicarboxylic acid dibutyl ester and an α-olefin; and (B) a thermal conductive filler filled in the base oil. The thermal conductive grease does not include conventionally used silicone oil so that insulating substances will not be formed in the thermal conductive grease.

BACKGROUND OF THE INVENTION

The present invention relates to a thermal conductive grease to be used for effectively radiating heat generated from electronic components.

Most of electronic components that are used in electronic and electric appliances generate heat during use. Accordingly, in order to obtain their proper functions, the removal of the heat generated may be required. Thus, heat conductive materials such as heat conductive greases and heat conductive sheets have been widely used in the art. For instance, a thermal conductive grease may be filled inbetween a heat-generating part of an electronic component and a cooling component or may be applied thereon to transfer the heat from the electronic component to the cooling component.

Thermal conductive grease which contains silicone oil as a base oil and inorganic powder as a thermal conductive filler has been widely known conventionally (see for example Japanese Laid-Open Patent Application 10-110179). However, in the case of using the thermal conductive grease containing silicone oil for the base oil, the silicone oil could sometimes separate or leach out of the grease, to thereby contaminate into its surroundings (see for example Japanese Laid-Open Patent Application 3-162493). In addition, as described in Japanese Laid-Open Patent Applications 3-106996 and 2002-201483, low-molecular weight siloxane that is contained in the silicone oil could precipitate as insulating materials such as silicon dioxide (SiO₂) and silicon carbide (SiC) by application of heat. Such insulators could malfunction the electronic appliances. Accordingly, another thermal conductive grease using oil other than silicone oil as the base oil has been proposed.

For improving the thermal conductivity of the thermal conductive grease, the base oil should be filled with the thermal conductive filler at high density. On the other hand, it turned out through a comparison between greases which have the same thermal conductivity and which are applied between the heat-generating part and the cooling component, that the thermal conductive grease could attain less thermal conductivity when the grease is applied with lower thickness, to thereby increase the thermal conduction. Therefore, from the viewpoint of thermal conduction, it is preferable to form a thin film of grease.

However, when the conventional thermal conductive grease provided as the base oil is filled with an inorganic powder at high density, the thermal conductive grease could have higher hardness to result in difficulty in forming into a thin film. As a result, the thermal resistance of the thermal conductive grease being applied was often inferior.

In particular, the grease that are filled with the thermal conductive filler at higher density had higher viscosity, and/or lower cone penetration (see Japanese Industrial Standard (JIS) K 2220), thereby resulting in poor dispensing properties of grease. In this case, the term “dispensing properties” refers to good workability for coating grease on a substrate, such as easiness of spreading the grease across the surface applied, fluidity and adherence of the grease thereon, and the like. Therefore, when the dispensing properties of the grease become inferior, it becomes difficult to discharge the grease from a coating applicator such as a syringe or it becomes difficult to spread the grease thinly on an exothermic body. Therefore, the compressibility of grease, which is an indicator of easiness in making a thin film of grease, decreases as the dispensing properties of grease decreases in a case where a fixed volume of grease is discharged on the contact surface and flattened out with a constant load.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a thermal conductive grease having excellent dispensing properties and an excellent compressibility as well as a high thermal conductivity attained by filling a base oil of a grease with a thermal conductive filler at high density.

According to a first aspect of the present invention, a thermal conductive grease is provided, comprising: (A) abase oil comprising a copolymer of an unsaturated dicarboxylic acid dibutyl ester and an α-olefin and having a viscosity of 112 to 770 mm² at 40° C.; and (B) a thermal conductive filler filled in the base oil.

In the first aspect of the invention, use of the copolymer of the unsaturated dicarboxylic acid dibutyl ester and the α-olefin provides the thermal conductive grease with more excellent dispensing properties and compressibility even when the thermal conductive grease is filled with the thermal conductive filler at high density. In addition, since silicone oil is not used as a base oil, troubles such as a contact fault due to scattering of low-molecular siloxane do not occur.

The thermal conductive grease can include copolymer that has a viscosity of 112 to 340 mm²/s at 40° C. The viscosity of the grease can be excellently proper in a case where the viscosity of the base oil falls in the range of 112 to 340 mm²/s.

The thermal conductive filler can be at least one or more selected from the group consisting of: zinc oxide; aluminum oxide; and boron nitride.

Further, the thermal conductive filler can be zinc oxide which is filled in the base oil at a percentage of 82 to 87.5 weight %.

The thermal conductive filler can be boron nitride which is filled in the base oil at a percentage of 47.6 weight % with respect to the base oil.

The thermal conductive filler can be aluminum oxide which is filled in the base oil at a percentage of 87.5 weight %.

According to the constructions described above, there may be provided with the thermal conductive grease having more excellent dispensing properties as well as higher thermal conductivity, compared with those of the conventional one.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a side view showing a schematic configuration of a thermal resistance measuring device.

DETAILED DESCRIPTION OF THE INVENTION

It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.

A thermal conductive grease as an embodiment of the present embodiment comprises: (A) a base oil comprising a copolymer of an unsaturated dicarboxylic acid dibutyl ester and an α-olefin, having a viscosity of 112 to 770 mm² at 40° C.; and (B) a thermal conductive filler filled in the base oil.

The thermal conductive grease of the present invention contains, as a base oil, 5 to 55 weight % of a copolymer of unsaturated dicarboxylic acid ester and α-olefin. Examples of the unsaturated dicarboxylic acid ester to be used include: esters of maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid. Among them, ester of maleic acid and fumaric acid is preferable. It is desirable that the alcohol component of unsaturated dicarboxylic acid ester has 3 to 10 carbon atoms. It is preferable that an unsaturated dicarboxylic acid dibutyl ester correspond to the unsaturated dicarboxylic acid ester because the thermal conductive grease attains good fluidity. The α-olefin preferably has 6 to 16 carbon atoms. In addition, a copolymer having an unbranched α-olefin shows a good fluidity even at low temperatures, so such the copolymer is preferred compared to one having a branched α-olefin.

The viscosity of the copolymer at 40° C. is 100 to 1,000 mm²/s, preferably 112 to 770 mm²/s, and more preferably 112 to 340 mm²/s, where the measurement is based on ASTM D-445. If the copolymer provided as a base oil has a viscosity of less than 112 mm²/s, the base oil easily separated from the obtained grease and thus it is not preferable. Furthermore, in the case where the viscosity is less than 112 mm²/s, the base oil is tend to be evaporated at high temperature. Thus, the content of oil in the grease may decrease so that crack, air layer, or the like may be formed at the contact surface with a cooling component, which then result in a decrease in thermal radiation characteristics. On the other hand, in the case where the copolymer used in the base oil has a viscosity exceeding 770 mm²/s, it becomes difficult to fill the base oil with an inorganic powder as a thermal conductive filler at high density. In addition, the dispensing property of the grease is decreased because of an increase of the viscosity.

The thermal conductive grease of the present invention as the thermal conductive filler contains an inorganic powder in an amount of 45 to 95 weight %. If the amount is less than 45 weight %, the grease cannot be provided with sufficient thermal radiation characteristics. In addition, if the amount is more than 95 weight %, the grease becomes excessively hard, thereby resulting in poor dispensing properties. Preferably, the inorganic powder is selected from a group consisting of zinc oxide, aluminum oxide, titanium oxide, magnesium oxide, silicon oxide, aluminum nitride, boron nitride, silicon nitride, silicon carbide, diamond, aluminum, silver, copper, and graphite, and combinations thereof. However, it is not limited to any of these material. Alternatively, one or more of other fillers may be used independently or in combination with any of the materials listed above. In addition, but not specifically limited to, the inorganic powder has an average particle size of preferably 20 μm or less, more preferably 5 μm or less. If the average particle size exceeds 20 μm, the compressibility of grease becomes inferior, thereby causing a decrease in thermal conductivity. Furthermore, two or more inorganic powders having different average particle sizes may be used in combination. In this case, also, the particle size distribution of the inorganic powder is not specifically limited. When electrical insulation properties are required in the thermal conductive grease, inorganic powder having electrical insulation properties can be generally used.

The thermal conductive grease of the present invention may contain a surfactant for improving the filling ability thereof. The addition of surfactant to the grease improves the filling rate of inorganic powder, thereby allowing an increase in thermal conductivity of the grease. Further, the addition of surfactant to the grease can impart more excellent dispensing properties and compressibility to the grease. Examples of the surfactant include non-ionic surfactant, anionic surfactant, cation surfactant, and amphoteric surfactant. The non-ionic surfactant does not effect on the electric characteristics of the grease, so it will be particularly preferable when the grease is expected to have electrical insulation properties. Examples of the non-ionic surfactant include polyoxyethylene oleyl ether and polyoxyethylene alkyl ether.

Further, if required, the thermal conductive grease may be mixed with any of various additives, including oxidation inhibitors, corrosion inhibitors, anticorrosive compositions, thickeners, puffing agents, pigments, dyes, antifoaming agents, plasticizers, and solvents.

The thermal conductive grease of the present invention can be obtained by mixing (A) a copolymer of unsaturated dicarboxylic acid ester and α-olefin, (B) an inorganic powder, and optionally a surfactant and any of various additives, in a mixer such as a planetary mixer and a trimix at room temperature or, if required, at elevated temperatures by heating. Furthermore, for mixing the mixture uniformly, the mixture may be mixed under high-shearing forces using a mixing device such as a three-roll mill or a colloid mill.

Hereinafter, the above embodiments will be described more specifically by way of examples and comparative examples, which do not intend to restrict the scope of the present invention.

EXAMPLE 1

With respect to: (A) 100 parts by weight (16.4 weight %) of a copolymer of unsaturated dicarboxylic acid dibutyl ester and α-olefin (trade name: Ketjenlube 115, manufactured by AKZO NOBEL Co., Ltd., having a viscosity of 112 mm²/s at 40° C.) as a copolymer of unsaturated dicarboxylic acid ester and α-olefin, (B) 500 parts by weight (82.0 weight %) of zinc oxide (0.4 μm in average particle size) as an inorganic powder and 10 parts by weight (1.6 weight %) of an non-ionic surfactant (polyoxyethylene oleyl ether) were introduced into a planetary mixer, and then stirred for one hour to be mixed, to obtain a thermal conductive grease.

EXAMPLE 2

A thermal conductive grease was prepared similarly as that of Example 1, except that the quantity of inorganic powder was increased. The weight percentages of copolymer and thermal conductive filler in a base oil are shown in Table 1, respectively.

EXAMPLE 3

A thermal conductive grease was prepared similarly as that of Example 1, except that the quantity of inorganic powder was increased. The weight percentages of copolymer and thermal conductive filler in a base oil are shown in Table 1, respectively.

EXAMPLE 4

With respect to 100 parts by weight (16.4 weight %) of a copolymer of unsaturated dicarboxylic acid dibutyl ester and α-olefin (trade name: Ketjenlube 135, manufactured by AKZO NOBEL Co., Ltd., having a viscosity of 340 mm²/s at 40° C.) as a copolymer of a base oil, 500 parts by weight (82.0 weight %) of zinc oxide (0.4 μm in average particle size) as an inorganic powder and 10 parts by weight (1.6 weight %) of an non-ionic surfactant were introduced into a planetary mixer, and then stirred for one hour to be mixed to obtain a thermal conductive grease.

EXAMPLE 5

With respect to 100 parts by weight (16.4 weight %) of a copolymer of unsaturated dicarboxylic acid dibutyl ester and α-olefin (trade name: Ketjenlube 215, manufactured by AKZO NOBEL Co., Ltd., having a viscosity of 120 mm²/s at 40° C.) as a copolymer of a base oil, 500 parts by weight (82.0 weight %) of zinc oxide (0.4 μm in average particle size) as an inorganic powder and 10 parts by weight (1.6 weight %) of an non-ionic surfactant were introduced into a planetary mixer, and then stirred for one hour to be mixed to obtain a thermal conductive grease.

EXAMPLE 6

With respect to 100 parts by weight (16.4 weight %) of a copolymer of unsaturated dicarboxylic acid dibutyl ester and α-olefin (trade name: Ketjenlube 165, manufactured by AKZO NOBEL Co., Ltd., having a viscosity of 770 mm²/s at 40° C.) as a copolymer of a base oil, 500 parts by weight (82.0 weight %) of zinc oxide (0.4 μm in average particle size) as an inorganic powder and 10 parts by weight (1.6 weight %) of an non-ionic surfactant were introduced into a planetary mixer, and then stirred for one hour to be mixed to obtain a thermal conductive grease.

EXAMPLE 7

As a copolymer of a base oil, 100 parts by weight (47.6 weight %) of Ketjenlube 115, which was the same as the one used in Examples 1 to 3, was used and as a thermal conductive filler, 100 parts by weight (47.6 weight %) of boron nitride (0.3 μm in average particle size) was used. Further, 10 parts by weight (4.8 weight %) of a non-ionic surfactant was used. The base oil, the thermal conductive filler, and the surfactant were introduced into a planetary mixer and then stirred for one hour to be mixed at room temperature, to obtain a thermal conductive grease.

EXAMPLE 8

As a copolymer of a base oil, 100 parts by weight (12.3 weight %) of Ketjenlube 115, which was the same as the one used in Examples 1 to 3, was used and as a thermal conductive filler, 700 parts by weight (87.5 weight %) of aluminum oxide (1 μm in average particle size) was used. Further, 10 parts by weight (1.2 weight %) of a non-ionic surfactant was used. The base oil, the thermal conductive filler, and the surfactant were introduced into a planetary mixer and then stirred for one hour to be mixed at room temperature to obtain a thermal conductive grease.

COMPARATIVE EXAMPLE 1

With respect to 100 parts by weight (16.4 weight %) of liquid polybutene “LV-50” (manufactured by Nippon Petrochemicals Co., Ltd., having a viscosity of 110 mm²/S at 40° C.) as a base oil, 500 parts by weight (82.0 weight %) of zinc oxide (0.4 μm in average particle size) as a thermal conductive filler and 10 parts by weight of a non-ionic surfactant were mixed and introduced into a planetary mixer, and then stirred for one hour to mix at room temperature, to obtain a thermal conductive grease.

COMPARATIVE EXAMPLE 2

With respect to 100 parts by weight (16.4 weight %) of ethylene α-olefin oligomer “HC-20” (manufactured by Mitsui Chemicals, Inc., having a viscosity of 155 mm²/S at 40° C.) as a base oil, 500 parts by weight (82.0 weight %) of zinc oxide (0.4 μm in average particle size) as a thermal conductive filler and 10 parts by weight of a non-ionic surfactant were mixed and introduced into a planetary mixer. The ingredients were stirred for one hour to be mixed at room temperature, to obtain a thermal conductive grease.

COMPARATIVE EXAMPLE 3

With respect to 100 parts by weight (16.4 weight %) of poly α-olefin “PAO10” (manufactured by Chevron Phillips Chemical Company LLC., having a viscosity of 65.3 mm²/S at 40° C.) as a base oil, 500 parts by weight (82.0 weight %) of zinc oxide (0.4 μm in average particle size) as a thermal conductive filler and 10 parts by weight of a non-ionic surfactant were mixed in a planetary mixer, and then stirred for one hour to be mixed at room temperature, to obtain a thermal conductive grease.

COMPARATIVE EXAMPLE 4

With respect to 100 parts by weight (16.4 weight %) of diphenyl ether “LB-100” (manufactured by Matsumura Oil Research, Co., Ltd., having a viscosity of 102 mm²/S at 40° C.) as a base oil, 500 parts by weight (82.0 weight %) of zinc oxide (0.4 μm in average particle size) as a thermal conductive filler and 10 parts by weight (1.6 weight %) of a non-ionic surfactant were mixed in a planetary mixer. The ingredients were stirred for one hour to be mixed at room temperature, to obtain a thermal conductive grease.

COMPARATIVE EXAMPLE 5

With respect to 100 parts by weight (47.6 weight %) of liquid polybutene “LV-50” (manufactured by Nippon Petrochemicals Co., Ltd., having a viscosity of 110 mm²/S at 40° C.) as a base oil, 100 parts by weight (47.6 weight %) of boron nitride (0.3 μm in average particle size) as an inorganic filler and 10 parts by weight (4.8 weight %) of a non-ionic surfactant were mixed in a planetary mixer. The ingredients were stirred for one hour to be mixed at room temperature, to obtain a thermal conductive grease.

COMPARATIVE EXAMPLE 6

With respect to 100 parts by weight (47.6 weight %) of ethylene α-olefin oligomer “HC-20” (manufactured by Mitsui Chemicals, Ltd., having a viscosity of 155 mm²/S at 40° C.) as a base oil, 100 parts by weight (47.6 weight %) of boron nitride (0.3 min average particle size) as an inorganic filler and 10 parts by weight (4.8 weight %) of a non-ionic surfactant were mixed in a planetary mixer. The ingredients were stirred for one hour to be mixed at room temperature, to obtain a thermal conductive grease.

COMPARATIVE EXAMPLE 7

With respect to 100 parts by weight (12.3 weight %) of liquid polybutene “LV-50” (manufactured by Nippon Petrochemicals Co., Ltd., having a viscosity of 110 mm²/S at 40° C.) as a base oil, 700 parts by weight (87.5 weight %) of boron nitride (1 μm in average particle size) as an aluminum oxide and 10 parts by weight (1.2 weight %) of a non-ionic surfactant were mixed in a planetary mixer. The ingredients were stirred for one hour to be mixed at room temperature, to obtain a thermal conductive grease.

COMPARATIVE EXAMPLE 8

With respect to 100 parts by weight (12.3 weight %) of ethylene α-olefin oligomer “HC-20” (manufactured by Mitsui Chemicals, Ltd., having a viscosity of 155 mm²/S at 40° C.) as a base oil, 700 parts by weight (87.5 weight %) of boron nitride (1 μm in average particle size) as an aluminum oxide and 10 parts by weight (1.2 weight %) of a non-ionic surfactant were mixed in a planetary mixer. The ingredients were stirred for one hour to be mixed at room temperature, to obtain a thermal conductive grease.

In Comparative Examples 1, 4, 5, and 7 described above, the thermal conductive greases were prepared by using the oligomers, which did not contain α-olefin, as base oils. As thermal conductive fillers, zinc oxide (Comparative Examples 1 and 4), boron nitride (Comparative Example 5), and aluminum oxide (Comparative Example 7), were respectively used.

In each of Comparative Examples 2, 3, 6, and 8, the thermal conductive greases were prepared by using the oligomer containing α-olefin as a base oil, however, the oligomer was not a copolymer of unsaturated dicarboxylic acid dibutyl ester and α-olefin. In addition, zinc oxide (Comparative Examples 2 and 3), boron nitride (Comparative Example 6), and aluminum oxide (Comparative Example 8) were also used, respectively, as thermal conductive fillers.

The characteristic features of the thermal conductive greases prepared by Examples 1 to 8 and Comparative Examples 1 to 8 were shown in Tables 1 and 2, respectively. For evaluating the characteristic features of the thermal conductive greases, the compressibility, dispensing properties, and thermal resistance were used as indicators. The compressibility was determined from the viscosity and one quarter scale penetration (see JIS-K2220; IS02137 “Petroleum products—Lubricating grease and petrolatum—Determination of cone penetration”; or ASTM D217-02 or D1403-02 “Standard Test Methods for Cone Penetration of Lubrication Grease Using One-Quarter and One-Half Scale Cone Equipment”). The dispensing properties was determined from the results of whether the grease could be actually discharged from a dispense nozzle (1.6 mm in opening diameter). The thermal resistance was determined by a method described below. Further details of the respective measurements for indicators will be described below.

The viscosity of grease was determined by using a Brookfield type rotational viscometer and calorific power Q at a rotating speed of 10 rpm at room temperature. The cone penetration of grease was determined by the method described in JIS-K2220 and represented as a numerical value indicated by the depth of grease reached by a conular probe immersed therein.

A thermal resistance measuring device as shown in FIG. 1 was employed for determination of thermal resistance. The detail of a thermal resistance measurement, which is based on ASTM D5470, is described below. A sample 10 was discharged onto a copper block 12 of 1 cm² in cross section mounted on a thermal insulating material 11 and then sandwiched with an upper copper block 13. Subsequently, the sample 10 was flattened by a weight 14 with a load of 4 kg. The thickness of the sample sufficiently flattened was measured. In the lower copper block 12, a heater (25 watts in calorific power, not shown) was installed. The upper copper block 13 is attached to a heat sink 15 with a fan to accelerate heat release. The heater was allowed to generate heat while the load was applied on the sample 10. Subsequently, when the temperature of the heat released has reached to a stationary state, then the temperatures of the upper copper block 12 and the lower copper block 13 were measured and the thermal resistance of the sample was then calculated from the equation (1).

Thermal resistance=(θj1−θj0)/calorific power Q  (1)

wherein θj1 represents the temperature of the lower copper block 12, θj0 represents the temperature of the upper copper block 13, and caloric power Q is 25 watts.

In this case, the compressibility of thermal conductive grease can also be evaluated by using the thickness of a sample when a given load is applied at the time of carrying out the thermal resistance measurement.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Base oil (weight %) Ketjenlube115 16.4 14.1 12.3 47.6 12.3 Ketjenlube135 16.4 Ketjenlube215 16.4 Ketjenlube165 16.4 Inorganic powder filler (weight %) Zinc oxide 82.0 84.5 87.5 82.0 82.0 82.0 Boron nitride 47.6 Aluminum oxide 87.5 Surfactant 1.6 1.4 1.2 1.6 1.6 1.6 4.8 1.2 (weight %) Viscosity of base oil 112 112 112 340 120 770 112 112 (mm²/s) (mm²/s) Viscosity of 82 91 172 91 116 326 331 138 grease (Pa · s) ¼ scale cone 92 86 80 79 89 71 62 86 penetration Dispensing Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent properties Sample thickness at 12 14 10 13 14 14 16 20 thermal resistance measurement (μm) Thermal resistance 0.15 0.14 0.13 0.14 0.14 0.14 0.20 0.20 (° C./W)

TABLE 2 Comparative Comparative Comparative Comparative Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Base oil (weight %) LV-50 16.4 47.6 12.3 H-20C 16.4 47.6 12.3 PA010 16.4 LB-100 16.4 Inorganic powder filler (weight %) Zinc oxide 82.0 82.0 82.0 82.0 Boron nitride 47.6 47.6 Aluminum oxide 87.5 87.5 Surfactant 1.6 1.6 1.6 1.6 4.8 4.8 1.2 1.2 (weight %) Viscosity of base oil 110 155 65.3 102 110 155 110 155 (mm²/s) Viscosity of grease 32 154 40 49 482 306 91 650 (Pa · s) ¼ scale cone 105 73 84 77 59 61 96 46 penetration Dispensing Excellent Excellent Excellent Excellent Excellent Excellent Excellent Poor properties Sample thickness at 23 22 22 24 27 32 31 38 thermal resistance measurement (μm) Thermal resistance 0.22 0.24 0.25 0.28 0.33 0.38 0.30 0.36 (° C./W)

The characteristic features of the respective thermal conductive greases represented in Tables 1 and 2 will be described in details.

Examples 1 to 6 and Comparative Examples 1 to 4 are compared, in which zinc oxide is used as a thermal conductive filler. In each of Examples 1 to 6, the thermal conductive grease having 0.15° C./W or less in thermal resistance, or excellent in thermal conductivity, while maintaining the viscosity and the cone penetration which can provide the grease with excellent compressibility, is obtained. In this case, the viscosity of the grease, which can provide the grease with good compressibility, is in the range of about 50 to 350 Pa·s in general. However, such a range is not always recommended and the compressibility of the grease may vary depending on materials even though the materials have the same viscosity. In Example 6 where the viscosity of the base oil is 770 mm²/s, the viscosity of the base oil is preferably in the range of 112 to 770 mm²/s, more preferably in the range of 112 to 340 mm²/s, because the viscosity of grease is higher than any of other examples. On the other hand, in any of Comparative examples 1 to 4, even though the grease obtained attains excellent dispensing properties, the thickness of the sample 10 is higher than any of the examples and insufficiently compressed. Therefore, it is revealed that the sample of any of the comparative examples has poor compressibility. Further, the thermal resistances of the samples of the comparative examples show 0.22° C./W or more, and the samples of the comparative examples have poor thermal conductivities in comparison with those of Examples 1 to 6.

Next, Example 7 and Comparative Examples 5 and 6 are compared, in which boron nitride is used as a thermal conductive filler. Both the examples and the comparative examples show good dispensing properties. However, in each of Comparative Examples 5 and 6, the compressibility of grease under the conditions in which the load is applied at the time of thermal resistance measurement shows poor compressibility, compared with that of Example 7. As a result, even though the thermal resistance of grease in the comparative example is higher than that of the comparative example, the grease having an excellent thermal conductivity with a thermal resistance of 0.20° C./W or less is obtained in the example.

Next, Example 8 and Comparative Examples 7 and 8 are compared, in which aluminum oxide is used as a thermal conductive filler. Example 8 shows excellent dispensing properties, while Comparative Example 8 shows poor dispensing properties. In addition, each of the comparative examples shows poor compressibility under the conditions in which the load is applied at the time of thermal resistance measurement, thereby resulting in higher thermal resistance. In Comparative Example 8, furthermore, the viscosity of grease is extremely high.

Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims. 

1. A thermal conductive grease comprising: (A) a base oil having a viscosity of 112 to 770 mm² at 40° C. and comprising a copolymer of an unsaturated dicarboxylic acid dibutyl ester and an α-olefin; and (B) a thermal conductive filler filled in the base oil.
 2. The thermal conductive grease according to claim 1 wherein the viscosity of said copolymer at 40° C. is in a range between 112 and 340 mm²/s.
 3. The thermal conductive grease according to claim 1 wherein said thermal conductive filler is selected from a group consisting of zinc oxide, aluminum oxide, boron nitride and combinations thereof.
 4. The thermal conductive grease according to claim 1 wherein said thermal conductive filler is zinc oxide and filled in the base oil in a range between 82 and 87.5 weight percent.
 5. The thermal conductive grease according to claim 1 wherein said thermal conductive filler is boron nitride and filled in the base oil at 47.6 weight percent.
 6. The thermal conductive grease according to claim 1 wherein said thermal conductive filler is aluminum oxide and filled in the base oil at 87.5 weight percent. 